Preparation And Photocatalytic Properties Of Polyoxometalate-Porphyrinic-MOFs Composites

The PCN-222 as porphyrinic-MOFs is selected in this paper.The PCN-222 has large specific surface area and good light response in the whole visible-light region.However,the photocatalytic performance of individual PCN-222 is poor due to rapid recombination of the photogenerated electron-hole pairs.Hence,the H₃PW₁₂O₄₀/PCN-222 composite is prepared via a one-step solvothermal method in this paper.The structure,composition and morphology of H₃PW₁₂O₄₀/PCN-222 are characterized by XRD,FT-IR and SEM.The optical properties of as-prepared catalysts are investigated via UV-Vis DRS.The degradation of RhB is carried out to evaluate the photocatalytic activity of catalysts under simulated sunlight and visible light irradiation.The 30 wt.%H₃PW₁₂O₄₀/PCN-222possesses the best photocatalytic properties.The degradation efficiency of RhB reaches99.46%after 150 min simulated sunlight irradiation and 79.88%after 300 min visible light irradiation,respectively.In order to further obtain highly-efficient visible-light-driven photocatalysts,PCN-222-PW₁₂/TiO₂ ternary composite material is prepared by solvothermal method.The structure,morphology and optical property of composites are studied by a series of characterizations.The 5 wt.%PCN-222-PW₁₂/TiO₂ displays superior photocatalytic properties.After 50 min simulated sunlight irradiation,99.2%RhB is degraded.After 80min visible light irradiation,98.5%RhB is removed and the degradation rate of 5 wt.%PCN-222-PW₁₂/TiO₂ is 4.69 times compared to PW₁₂/TiO₂.In order to avoid the photosensitizing effect of dyes and explore photocatalytic capacity of PCN-222-PW₁₂/TiO₂,the degradation experiments of Ofloxacin are carried out.Similar to the photodegradation process of RhB,PCN-222-PW₁₂/TiO₂ composite also displays superior photocatalytic activity in the degradation of Ofloxacin compared to pure PCN-222 and PW₁₂/TiO₂.The result reveals that 97.72%Ofloxacin is degraded after 60min simulated sunlight irradiation and 94.48%Ofloxacin is removed after 120 min visible light irradiation.The PCN-222-PW₁₂/TiO₂ catalyst decreases slightly in four cycles under visible-light irradiation.By changing the initial concentration of Ofloxacin and pH,the effect on degradation efficiency is investigated.The results show that the PCN-222-PW₁₂/TiO₂ has best degradation rate at the initial concentration of ofloxacin 5mg/L and pH=1.Pure TiO₂ system has only two active species,including^·O₂^-and h⁺_VB.The active species trapping experiments shows that PCN-222-PW12/TiO2 system has three active species,including^·OH radical,^·O₂^-and h⁺_VB,which may be additional evidence for the enhanced photocatalytic activity of PCN-222-PW₁₂/TiO₂ with respect to pristine TiO₂.